Magnetic-field dependence of superconducting energy gaps in $\mathrm{Y}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$: Evidence of multiband superconductivity

Magnetic-field dependence of superconducting energy gaps in $Y {Ni}_{2} B_{2} C$ : Evidence of multiband superconductivity

S. Mukhopadhyay, Goutam Sheet, P. Raychaudhuri, and H. Takeya

Phys. Rev. B 72, 014545 – Published 27 July 2005

Abstract

We present results of an in-field directional point-contact spectroscopy study of the quaternary borocarbide superconductor $Y {Ni}_{2} B_{2} C$ , which is characterized by a highly anisotropic superconducting gap function. For $I ‖ a$ , the superconducting energy gap $(Δ)$ , decreases linearly with magnetic field and vanishes at around $3.25 T$ , which is well below the upper critical field $(H_{c 2} \sim 6 T)$ measured at the same temperature $(2 K)$ . For $I ‖ c$ , on the other hand, $Δ$ decreases weakly with magnetic field but the broadening parameter $(Γ)$ increases rapidly with magnetic field with the absence of any resolvable feature above $3.5 T$ . From an analysis of the field variation of energy gaps and the zero-bias density of states we show that the unconventional gap function observed in this material could originate from multiband superconductivity.